1. Field of the Invention
The present invention relates to a control method for a suspension which is provided to a vehicle such as an automobile or the like, and more particularly relates to a control method for a suspension which is equipped with actuators which apply forces in the upwards and downwards directions to the vehicle wheels.
2. Background Art
A suspension which is fitted to a vehicle fulfills the role of giving the vehicle a more comfortable ride by absorbing shocks from the road surface with which the vehicle wheels are in contact, and generally comprises coil springs and shock absorbers which suppress vibrations of these coil springs. There is a tendency that, the smaller is the spring rate of these coil springs with which the suspension is equipped and the softer are the springs, the better is the comfort of the ride.
On the other hand, although the greater is the stiffness of the vehicle body the greater is the controllability of the vehicle, if the spring rate is reduced in order to enhance the comfort of the ride, not only can rolling when steering the vehicle round a curve, or pitching during acceleration or deceleration, easily occur, but the controllability has a tendency to decrease; and, furthermore, since the vehicle body tilts from the point of view of the passengers, it cannot be said that the comfort of the ride is good.
Since in this manner, with a conventional vehicle suspension, it is difficult to improve both the controllability and also the comfort of the ride simultaneously, therefore it often happens that the suspension characteristics are set to give either excellent ride comfort or excellent controllability, according to the character which it is desired the vehicle should possess.
In the prior art, it is known to provide a stabilizer for enhancing the roll stiffness of the vehicle body. Such a stabilizer has no function of acting as a spring when both the left wheel and the right wheel between which it is fitted move in the same sense; but, when this left wheel and right wheel move in opposite senses, one upwards and one downwards, as during rolling of the vehicle body, the stabilizer suppresses this rolling by acting as a spring. Since the stabilizer acts as a spring when the left wheel and the right wheel move in opposite senses, it becomes possible to suppress rolling without increasing the spring rate of the coil springs of the vehicle.
Moreover, since it is easy for rolling to occur when the vehicle is being steered around a curve if the ride comfort is enhanced by reducing the spring rate of the coil springs, accordingly in this case it is necessary to increase the reaction force which is generated by the stabilizer bar, either by increasing the diameter of the stabilizer bar, or by reducing the length of the portion thereof in which twisting takes place, or the like.
However, if the reaction force which is generated by the stabilizer bar is increased, then, as a result, this is equivalent to the case in which the spring rate of the coil springs is increased in circumstances in which the road surface upon which the vehicle is being driven has irregular convexities and concavities, and therefore there is the problem that there is a tendency for the comfort of the ride to be deteriorated.
The objective of the present invention is to provide a control method for a vehicle suspension which, by implementing control of actuators which apply forces in the upwards and downwards directions to the vehicle wheels according to the operational conditions of the vehicle, can simultaneously enhance both the control stability of the vehicle and also the comfort of the ride for the passengers in the vehicle.
According to a first aspect of the present invention, there is proposed a suspension control method for controlling a suspension which includes respective actuators for left and right wheels of a vehicle, and which can apply forces in the upwards and downwards direction to the left and right vehicle wheels via these actuators, wherein, while the vehicle is being driven in a straight line, control is performed by giving priority to ride comfort (for example, by skyhook control); and, while the vehicle is being driven around a curve, control is performed by giving priority to roll suppression (for example, by rolling suppression control).
According to this aspect of the present invention as described above, it is possible to reduce vibration of the vehicle body when the vehicle is being driven in a straight line, while, when the vehicle is being driven around a curve, it is possible to reduce tilting of the vehicle body, so that it is possible to enhance the comfort of the ride from the point of view of the vehicle occupants. Furthermore, it becomes possible to enhance both the control stability and also the comfort of the ride in a compatible manner, since it becomes possible to increase the apparent spring rate only when the vehicle is being driven around a curve.
In the above described suspension control method, it is desirable, if the acceleration in the forwards and rearwards direction of the vehicle is greater than a predetermined value, to perform control by giving priority to pitching suppression, even while the vehicle is being driven in a straight line.
In this case, by performing control by giving priority to pitching suppression if the acceleration in the forwards and rearwards direction of the vehicle is greater than the predetermined value, even while the vehicle is being driven in a straight line, it becomes possible to reduce tilting of the vehicle body in the forwards and rearwards direction, and it accordingly becomes possible to enhance the comfort of the ride from the point of view of the passengers in the vehicle. Furthermore, it becomes possible to enhance both the control stability and also the comfort of the ride in a compatible manner, since it becomes possible to increase the apparent spring rate only during acceleration or deceleration.
In the above described suspension control method, it is also desirable to vary the forces generated by the actuators according to the speed of the vehicle. In this case, it becomes possible to prevent deterioration of the comfort of the ride, since the forces generated by the actuators are varied according to the speed of the vehicle, and at low vehicle speed it becomes possible to perform control more minutely due to elimination of influences from convexities and concavities of the road surface.
Moreover, according to another aspect of the present invention, there is proposed a suspension control method as first described above, in which the acceleration of the vehicle in the upwards and downwards direction is detected, and, if the value of this upwards and downwards acceleration falls outside a predetermined range of values, and moreover has continued to be outside the predetermined value range for longer than a predetermined time period, then control is performed to suppress vibration of the vehicle based upon the value of the upwards and downwards acceleration which is detected.
According to this aspect of the present invention, if the change of acceleration in the upwards and downwards direction is rapid, it is possible to prevent vibration suppression control being performed for the vehicle body based upon the detected value of acceleration in the upwards and downwards direction, and as a result the comfort of the ride at this time is enhanced.
According to another aspect of the present invention, there is proposed a suspension control method as first described above, in which the acceleration of the vehicle in the upwards and downwards direction is detected, and, if the value of this upwards and downwards acceleration falls within a predetermined range of values, and moreover has continued to be within the predetermined value range for longer than a predetermined time period, then control (for example, skyhook control) is not performed to suppress vibration of the vehicle based upon the value of the upwards and downwards acceleration which is detected.
According to this aspect of the present invention, in the case of minute change of acceleration in the upwards and downwards direction, vibration suppression control for the vehicle body is not performed, and as a result it is possible further to enhance the comfort of the ride upon road surfaces for which the stroke of the suspension is small.
Another aspect of the present invention has as its objective to suppress the generation of inconveniences such as the generation of vibration or the like during electrical current feedback control of the electromagnetic actuator, so as to enhance the efficiency of convergence of the actual electrical current value to the target electrical current value when supplying electrical current to the actuator.
In order to achieve the above described objective, this aspect of the present invention proposes a control method for an electromagnetic actuator, including: a step of, when supplying electrical current to the electromagnetic actuator to generate a desired output, calculating a first duty ratio for the electrical current to be supplied to the electromagnetic actuator corresponding to a target electrical current value for the electrical current; a step of calculating a second duty ratio for the electrical current to converge the actual electrical current value which flows through the electromagnetic actuator to the target electrical current value by proportional integral and differential control; and a step of supplying electrical current to the electromagnetic actuator according to a third duty ratio which is obtained by adding together the first duty ratio and the second duty ratio.
According to this aspect of the present invention, in the proportional integral and differential control of the electromagnetic actuator, first a first duty ratio for the electrical current to be supplied to the electromagnetic actuator from a power source device or the like is calculated corresponding to a target electrical current value. Then the actual electrical current value which flows through the electromagnetic actuator is detected, and a second duty ratio is calculated for proportional integral and differential control to converge this obtained actual electrical current value to the target electrical current value. This second duty ratio and the first duty ratio are added together to produce a third duty ratio, and electrical current is supplied to the electromagnetic actuator according to this third duty ratio.
In other words, when calculating this third duty ratio which is referred to when supplying electrical current to the electromagnetic actuator, it is possible to reduce the contribution of the second duty ratio which is calculated for PID control by calculating the first duty ratio according to the target electrical current value. Due to this, the proportional term for PID control can be made smaller, and accordingly it is possible to suppress inconveniences such as the generation of vibration or the like during feedback control, and it is possible to improve the efficiency of convergence of the actual electrical current value to the target electrical current value.
According to yet another aspect of the present invention, there is proposed a control device for an electromagnetic actuator, including: a target electrical current value calculation device which, when supplying electrical current from a power source device to the electromagnetic actuator to generate a desired output, calculates a target electrical current value for the electrical current; a first duty ratio calculation device which calculates a first duty ratio for the electrical current to be supplied from the power source device to the electromagnetic actuator corresponding to the target electrical current value; an electrical current detection device which detects the actual electrical current which flows through the electromagnetic actuator and obtains an actual electrical current value; a second duty ratio calculating device which calculates a second duty ratio for the electrical current to converge the actual electrical current value to the target electrical current value by proportional integral and differential control; and a current control device which supplies electrical current from the power source device to the electromagnetic actuator according to a third duty ratio which is obtained by adding together the first duty ratio and the second duty ratio.
According to this aspect of the present invention, during the proportional integral and differential control of the electromagnetic actuator, first, the first duty ratio for the electrical current to be supplied from the power source device to the electromagnetic actuator is calculated based upon the target electrical current value. Then the actual electrical current value which flows through the electromagnetic actuator is detected, and a second duty ratio is calculated for proportional integral and differential control to converge this obtained actual electrical current value to the target electrical current value. This second duty ratio and the first duty ratio are added together to produce a third duty ratio, and electrical current is supplied to the electromagnetic actuator according to this third duty ratio.
Due to this, it is possible to reduce the proportional term for PID control, and accordingly it is possible to suppress inconveniences such as the generation of vibration or the like during feedback control, and it is possible to improve the efficiency of convergence of the actual electrical current value to the target electrical current value. In particular, if for example a predetermined output is connected to the electromagnetic actuator, by setting the first duty ratio which has been calculated from the target electrical current value as a so called standard value, and by performing PID control for the amount of deviation from this standard value, since it is possible to set the constant of proportionality to a relatively small value, thereby it is possible easily to maintain the desired output.
A yet further aspect of the present invention takes as its objective to provide a control method which, when the vehicle is being driven in a zigzag course or the like, and abrupt changes in the rolling direction are occurring, can attain suitable roll stiffness corresponding to the roll angle.
In order to achieve the above described objective, this aspect of the present invention proposes an actuator control method in which a difference between amounts of movement of left and right wheels of the vehicle in the upwards and downwards direction is detected, and a rate of change of steering angle is detected, and actuators are controlled based upon the vehicle wheel movement amount difference and upon the rate of change of steering angle. By doing this, including the case in which the vehicle body is at its central position, torque is generated based upon the speed by which the steering wheel is being rotated, in other words upon the rate of change of the steering angle, and torque control for the actuator is performed in the opposite direction to the rolling direction based upon this torque, so that the reverse wheel rate is increased. Accordingly, by comparison to the case in which the control is based only upon the variation of stroke amount, the roll stiffness during cornering is complemented and the initial responsiveness is enhanced, and it is possible to improve the response lag due to the compliance of the vehicle, and moreover, it is possible to position the center of gravity of the vehicle body at its geometrical center from the start of cornering, and stability of the vehicle is obtained with regard to the centrifugal force which is generated during cornering.
According to a yet further aspect of the present invention, there is proposed a suspension control method as described above, in which a stabilizer is provided which mechanically links together the left and right vehicle wheels, and which generates torque according to the difference between the movement amounts of the left and right vehicle wheels in the upwards and downwards direction with respect to the vehicle body; and in which deficiency of force to suppress rolling of the vehicle body is, as required, supplemented by the actuators.
Since with this control method, while the vehicle is being driven in a straight line and the steering wheel is not being actuated, a rate of change of steering angle of xe2x80x9c0xe2x80x9d is obtained, and moreover a difference of xe2x80x9c0xe2x80x9d in the movement amounts of the vehicle wheels with respect to the vehicle body due to rolling is obtained, accordingly at this time the control circuit does not control the actuators, and since the stiffness of the suspension is not complemented, the suspension operates according to the inherent standard values of the spring rates of the stabilizer and the springs, so that the original ride comfort which has been set in advance is not lost.
The spring rate which determines the roll stiffness of the vehicle body is both the spring rates of the springs of the suspension and also a spring rate based upon the torsional stiffness of the stabilizer, but in the following, for convenience of explanation, the spring rate of the stabilizer will be described as being included in the spring rates of the springs.
According to a yet further aspect of the present invention, there is proposed an actuator control method in which sidewise acceleration of the vehicle body is detected, and the actuator is controlled according to the sidewise acceleration and upon rate of change of steering angle. In this case, including the case in which the vehicle body is at its central position, torque is generated based upon the speed by which the steering wheel is being rotated, in other words upon the rate of change of the steering angle, and torque control for the actuator is performed in the opposite direction to the rolling direction based upon this torque, so that the reverse wheel rate is increased. Accordingly, by comparison to the case in which the control is based only upon the variation of stroke amount, the roll stiffness during cornering is complemented and the initial responsiveness is enhanced, and it is possible to improve the response lag due to the compliance of the vehicle, and moreover, it is possible to position the center of gravity of the vehicle body at its geometrical center from the start of cornering, and stability of the vehicle is always obtained with regard to the centrifugal force which is generated during cornering.
Furthermore, since in this suspension control method the control of the actuators utilizes the sidewise acceleration, instead of the difference in the movement amounts of the vehicle wheels with respect to the vehicle body, and accordingly no stroke sensors are employed but instead the sidewise acceleration sensor is used, therefore, by comparison to the case in which stroke sensors are employed, it is possible to eliminate the two high cost stroke sensors which otherwise would need to be provided to the left and right vehicle wheels, and moreover, since no links or rods from the drive arms to any stroke sensors are required, accordingly it is possible to simplify the system as a whole due to simplification of the structure of the detection mechanism which detects the operational state of the vehicle body, and it becomes possible to reduce the cost of its construction.
In a suspension control method according to a yet further aspect of the present invention, when the roll direction of the vehicle and the steering speed direction are the same, control is performed based upon the vehicle wheel movement amount difference with respect to the vehicle body, and upon the rate of change of steering angle. However, when the roll direction of the vehicle and the steering speed direction are not the same, control is performed based upon the vehicle wheel movement amount difference with respect to the vehicle body. Moreover, in the central state when the amount of rolling of the vehicle body is small, without any dependence upon whether or not the roll direction of the vehicle and the steering speed direction are the same, control is performed based upon the vehicle wheel movement amount difference with respect to the vehicle body, and upon the rate of change of steering angle. In other words, by compulsorily adding the torque based upon the rate of change of steering angle which is the differential coefficient of the steering angle amount, to the torque which is obtained from the difference in the movement amounts of the left and right vehicle wheels with respect to the vehicle body, thereby the lag of control of the vehicle body in the transient cornering state is complemented by the torque which is obtained from the rate of change of the steering angle, and the response speed during turning for initial cornering is improved; and, moreover, during anti-rolling control, it becomes possible to enhance the reaction to rolling during initial cornering, without generating lag in the control of the vehicle body, based upon the lag of the control system for the actuators or the like, and upon the vehicle compliance.
In a suspension control method according to a yet further aspect of the present invention, when the roll direction of the vehicle and the steering speed direction are the same, control is performed based upon the sidewise acceleration and upon the rate of change of steering angle; and, when the roll direction of the vehicle and the steering speed direction are not the same, control is performed based upon the sidewise acceleration; while, in the central state when the amount of rolling of the vehicle body is small, without any dependence upon whether or not the roll direction of the vehicle and the steering direction are the same, control is performed based upon the sidewise acceleration of the vehicle wheels with respect to the vehicle body, and upon the rate of change of steering angle. In other words, by compulsorily adding the torque based upon the rate of change of the steering angle which is the differential coefficient of the steering angle amount, to the torque which is obtained from the sidewise acceleration, thereby the lag of control of the vehicle body in the transient cornering state is complemented by the torque which is obtained from the rate of change of steering angle, and the response speed during turning for initial cornering is improved. Accordingly, during anti-rolling control, it becomes possible to enhance the reaction to rolling during initial cornering, without generating lag in the control of the vehicle body, based upon the lag of the control system for the actuators or the like, and upon the vehicle compliance.
Moreover, in a suspension control method according to a yet further aspect of the present invention, in the above suspension control methods, when determining upon the central state, the decision is made utilizing hysteresis, so that it is possible to prevent hunting of the vehicle operational state value, as compared to the case in which the threshold value is a single point, where, when the difference in the movement amounts of the left and right vehicle wheels with respect to the vehicle body varies around the threshold value, significant hunting is generated. Due to this, since it is possible to avoid instability of the control of the actuators due to oscillation of the vehicle operational state value because the electrical current value which is supplied to the actuators is supplied stably without hunting occurring, accordingly the convergence performance to the rolling state of the torques which are generated by the actuators is improved, and the benefit is obtained that the responsiveness of control of the roll stiffness of the suspension is improved. Furthermore, since it is possible to prevent hunting due to change of the above described stroke positions around their central states, the behavior of the vehicle body is stabilized, since there is no vibration of the vehicle body due to the hypersensitive influence of minute changes during anti-rolling control of the vehicle body.